The present invention relates generally to the production of laminated paper products and more particularly to a method of lamination and a device for laminating a continuous roll of extensible plastic film material to a continuous roll of paper backing material wherein the device has a system for controlling the amount of distortion in the plastic film material to ensure proper registry of the film material with the paper material.
Lamination of a plastic film material to a paper material has been found to be particularly advantageous where paper products having high strength and abrasion resistant qualities are required. Such laminated composites are particularly desirable in the packaging industry where artwork may be printed on the interior side of the plastic film to produce a high quality display package. The construction and use of such laminated composites are described in Peer U. S. Pat. No. 4,254,173, which is hereby incorporated by reference.
In producing a laminated composite of the type described in Peer, both the plastic film material and the paper material may be provided in continuous sheets, usually referred to as "webs," which are mounted on spools. The paper and the plastic film generally pass over a number of roller type devices where each of the materials is independently stretched under tension and treated in a manner dependent upon the particular end use for the laminated composite. For example, the plastic material may be irradiated in conventional processes to increase its strength or to improve its printability. In preferred embodiments, the plastic is printed with various graphics and provided with a metalized background to enhance the package appearance. The paper as well may undergo treatment such as being electrostatically charged to aid in the bonding process. Either the film material or the paper material or both are treated with suitable adhesive to provide a bond between the paper and the film. To complete the laminating process, the paper and film materials are pressed together between opposed rollers to produce a smooth, flat composite. Various heating or cooling processes may also be required to ensure proper adhesion of the surfaces, depending upon the type of film, paper, and adhesive agent which is being used in the process. The end product of the process is a laminated composite which may be fed directly to a die cutter or to other machines for further processing. The composite may also be taken up directly on a separate spool for storage and later processing.
Use of the film paper composite provides many advantages over conventional packaging material but also creates some unique problems. In order to be cost effective, the plastic material used is generally quite thin--on the order of 0.25-to-2.0 mils. Plastic films of such thicknesses tend to stretch or shrink during the lamination process as a result of variations in temperature and the varying inertial forces exerted on the film as it is unrolled and processed prior to bonding with the paper. Such stretching and shrinking may cause warping or buckling in the laminated composite as the film returns to a steady-state condition. Similarly, a printed image may be repeated on the film for later lamination in registry with predetermined lengths of paper material. In such cases, the printed image length must be held within close tolerance in order to permit proper registry with other processing activities such as automated cutting in a later process step.
Thus, it can be seen that a need exists for a paper-film laminating device which is capable of controlling the amount of stretching distortion in the plastic film material prior to lamination.
Apparatus for controlling the amount of longitudinal stretch in a web of plastic film being laminated to a web of paper board are disclosed in U.S. patent application Ser. No. 441,276 filed Nov. 12, 1982, for CONTROL STRETCH LAMINATING DEVICE of Joseph Robert Haake, Tracy Jay Fowler, and James Wendell Jensen, now U.S. Pat. No. 4,496,417 and U.S. patent application Ser. No. 624,480 filed June 22, 1984, for CONTROL STRETCH LAMINATING DEVICE of James Wendell Jensen and Joseph Robert Haake, now U.S. Pat. No. 4,572,752, both of which are hereby incorporated by reference for all that is contained therein.
It has been found that in some applications it is necessary to accurately control the lateral as well as the longitudinal deformation of a moving film web. Lateral deformation control is especially important when the amount of longitudinal deformation of the film web is relatively large, since longitudinal stretching tends to cause the film web to shrink in its lateral dimension at a rate approximately predictable by Poisson's Ratio for the particular film web material being used.
It would thus be desirable to provide an apparatus capable of controlling lateral as well as longitudinal material in a moving film web.